MODELING THE PHYSIOLOGICAL COST OF NITROGEN FIXATION: WHY DO DIAZOTROPHS GROW SLOWLY?
Nitrogen fixation relieves organisms of limitation by fixed nitrogen sources but has a high penalty due to low growth rates. In order to understand and model the ecology of nitrogen fixation in the ocean, we must quantify that cost. As a first step, we have developed a simplified metabolic flux model of a diazotrophic bacteria using mass, redox, and energy balance constraints. We test and constrain the model using the plentiful physiological and energetic data for the heterotrophic, nitrogen-fixing soil bacterium Azotobacter vinelandii. Enforcing energy balance, the model shows that the direct energetic cost of nitrogen fixation is not the main cause of the slow growth rate. Breaking energy balance, but demanding low intra-cellular O2 concentration by enhanced respiration explains the inefficiency of growth. The framework provides the basis a model of marine nitrogen fixation with which we evaluate the role of cell size and symbiotic relationships for the ecology of marine nitrogen fixation. We will illustrate these consequences in the context of an ocean circulation and biogeochemistry model.
Inomura, K., Massachusetts Institute of Technology, USA, email@example.com
Follows, M. J., Massachusetts Institute of Technology, USA, firstname.lastname@example.org
Location: 323 ABC
Presentation is given by student: Yes